Photophysical Properties and Efficient, Stable, Electrogenerated Chemiluminescence of Donor–Acceptor Molecules Exhibiting Thermal Spin Upconversion

Abstract

The photophysical properties and electrogenerated chemiluminescence (ECL) of three donor-acceptor molecules composed of dicyanobenzene and methyl-, tert-butyl-, and phenyl-substituted carbazolyl groups, 1,2,3,5-tetrakis(3,6-disubstituted-carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN-Me, 4CzIPN-tBu, and 4CzIPN-Ph, respectively) are described. These molecules show delayed fluorescence as a result of thermal spin upconversion from the lowest triplet state to the lowest singlet state at room temperature. The three molecules showed yellow to yellowish-red ECL. Remarkably, the ECL efficiencies of 4CzIPN-tBu in dichloromethane reached almost 40 %. Moreover, stable ECL was emitted from 4CzIPN-tBu and 4CzIPN-Ph. In case of 4CzIPN-Me, the ECL intensity decreased during voltage cycles because of polymerization. Quantum chemical calculations revealed that polymerization was inhibited by the steric hindrance of the bulky tert-butyl and phenyl groups on the carbazolyl moieties and lowered the spin density on the carbazolyl groups through electron conjugation for 4CzIPN-Ph.

Why were alternating-current-driven electrochemiluminescence properties from Ru(bpy)32+ dramatically improved by the addition of titanium dioxide nanoparticles?

“…[1][2][3][4] ECL mechanisms are typically categorized as co-reactant-or annihilation-based ECL processes. [10][11][12][13][14][15] We have focused on the annihilation ECL system to develop a light-emitting device having various advantages as follows. This phenomenon has been widely investigated since it can be applied in chemical and bio-sensor devices.…”

Homogeneous Electron Transfer Reactions of Electrochemically Generated Species in Electrogenerated Chemiluminescence

“…G 0 (S1) = −0.6 eV, G 0 (T1) = −1.6 eV とする と ket(S1) / ket(T1) 22) 。 ECL の効率は，Ru(bpy)3 2+ や 9,10-ジフェニ ルアントラセン(DPA)などの基準物質 26,27)…”

Electrochemical Generation of Excited Intramolecular Charge‐Transfer States

“…Among already reported A−D n or D−A n molecules the previously mentioned bis(carbazole‐9‐yl) and tetrakis(carbazole‐9yl) derivatives of aromatic nitriles (phthalonitrile, isophthalonitrile and terephthalonitrile) are especially exciting . These molecules (with structures schematically presented in Figure ) form relative stable radical anion − A−D n and cation A−(D n ) + with the unpaired electron localized (in the view of the DFT quantum‐mechanical calculation) within the acceptor subunit or uniformly redistributed over two or four donor subunits . Relatively large solvatochromic effects observed in their emission properties point to the CT nature of their excited 1 *[ − A−(D n ) + ] states.…”